feat: command line shell modifiers

[sammy-ette]

if hilbish input begins with @ it can be used to modify certain things about the input to be ran.
this idea just randomly came in my mind, i can't really think of a use case currently but i don't want to forget the idea.

example @opt=value ls ~

maybe this can be used to set hilbish.opts temporarily (only for this command?)

[sammy-ette]

@dir=./directory changes directory temporarily.. easier than remembering to do cd ./dir && command && cd -